Generally speaking anchors are bodies that have a series of slips that are retracted for running into a desired location and then have the slips extended to grip in the wellbore to support a tool or a string of tubulars or other downhole equipment. The objective in anchor design is to allow the tool to have the slimmest profile for insertion and then extend as much as possible for a grip, where the grip will still be strong enough to resist the anticipated loads.
U.S. Pat. No. 7,114,559 shows an anchor design in FIG. 2. The present invention is an improvement to that design. For completeness in understanding this invention FIGS. 1 and 2 will illustrate the preferred embodiment in the prior application to better provide a framework to understanding the present invention.
Thus, by way of background, FIGS. 1 and 2 will be reviewed to get an understanding of the present invention that has simply resulted in being able to extend the reach of an anchor for a given run in drift diameter to further than is possible with the design of FIGS. 1 and 2. FIG. 1 is a split view showing a slip in a retracted position for run in on the top half of the drawing and the same slip 10 in an extended position on the bottom half of FIG. 1. A jagged section line 2-2 in Figure indicates where on FIG. 1 the section shown in FIG. 2 is taken. What is shown is a mandrel 12 that has a series of ramps 14, 16 and 18. The mandrel 12 has a passage 20 through which pressure is put on a piston (not shown) that causes relative movement between the mandrel 12 and the slips 10 that are mounted to it. The mandrel 12 is shown to be symmetrical about the center line 22.
Slip 10 has ramps 24, 26 and 28 that rest against ramps 14, 16 and 18 for run in to create the smaller profile shown in FIG. 1. The inserts 30 stick out the most during run in and define the drift diameter necessary for the tool to pass on run in. The mandrel 12 has peaks set apart from each other and two of them 32 and 34 are shown in FIG. 1 that are disposed above and below ramp 16 for illustrative purposes. The slip 10 is an integral structure that spans over the ramps 14, 16 and 18 and is designed to have thin connecting segments such as 36 and 38 that meet design criteria. The Anchor design needs to consider the load to be applied, such as tensile loads through the mandrel 12, bearing area on slip 10 and ramp 16, and tensile loads through slip 10. Also, this should be designed within a small cross section dictated by the amount of travel needed. The segments 36 and 38 need to be thin to allow the tool to get through the smallest drift dimension possible. This is because the slips 10 are mounted fully over the mandrel 12 and the thicker they get in the connecting segments such as 36 and 38 the greater the drift will be required to run the tool downhole. The limiting value on how thin the segments 36 and 38 can get is how much tension load they have to take as the slip 10 rides out on the ramps on the mandrel 12. If the slip 10 doesn't move exactly evenly in its radial motion one or more segments get put under a temporary tensile load. Thus the segments must have sufficient cross-section to avoid failure from stressing during setting. The setting occurs when pressure is applied to passage 20 and relative movement of the slip segments 10 occurs with respect to mandrel 12. FIG. 2 shows a section view of the slip segment 10 retracted at the top and extended at the bottom. The section view is through the thin segment 36 shown in FIG. 1. Looking at the bottom of FIG. 1, it is easier to see that the most highly stressed portion of the slip 10 is at the thin segments such as 36 and 38 or the bearing area remaining between ramp 16 and slip 10. Ideally, the slip 10 has upper and lower ends that move in tandem in a radial direction but in reality due to irregularities in the surrounding tubular some portion of the slip 10 can engage at a different time than another portion to stress the thin segments such as 36 or 38.
Those skilled in the art will appreciate that although only a single slip 10 is shown in two positions in a split view that mandrel 12 supports a series of slips 10 around its circumference that are retained in a retracted position by one or more band springs (not shown).
The present invention optimizes the profile of the anchor so that the required drift dimension to run it in is kept to a minimum, while at the same time making it possible to extend the slips further into a larger tubular than the previous design and still get a good bite for support downhole. These and other aspects of the present invention will be more readily apparent to those skilled in the art from reviewing the description of the preferred embodiment and the drawings along with the claims, which are the full measure of the invention.